The present invention relates to lubricants for transmissions which include a synchronizer with a non-metallic surface. Such lubricants show improved performance with non-metal synchromesh components. Problems occur with synchromesh parts in transmissions which include a synchronizer with a non-metallic surface with many oils delivering a non-optimal friction.
A synchronizer is one of the more important components of manual and dual clutch transmissions. Increasing performance, reducing shift force and minimizing the between-the-gears energy losses are the primary objectives for a new generation of synchronizer systems. Improvements in the capacity of the mechanical system and the introduction of various synchronizers of various designs and materials are allowing economical re-engineering of existing synchronizer designs into more efficient designs. The lubricants or additives for manual and dual clutch transmission lubricating oils needs to be reformulated for these designs to be able to maintain adequate friction between the interacting parts of the synchronizer and to protect these parts from wear.
Conventional gear oils or manual transmission oils typically contain chemical components, such as active sulfur and surface-active amine organophosphates. While excellent as additives to provide extreme pressure lubrication, in the usual amounts these additives alone are typically too slippery and do not adequately protect the lubricated surfaces from abrasive or corrosive wear.
U.S. Pat. No. 6,503,872, Tomaro, Jan. 7, 2003, discloses extended drain manual transmission lubricants which contain at least one basic alkali or alkaline earth metal salt of an acidic organic compound. The overbased material generally have a total base number up to about 600 or about 500, or about 400. In Example 1, a manual transmission lubricant is prepared by blending into a manual transmission base stock, 1.2 parts of the Example A-6 [a metal dithiophosphate] with 0.4 parts of an oil solution of an overbased magnesium sulfonate (42% diluent oil, metal ratio 14.7, 9.4% magnesium, and 400 total base number) to form an intermediate, to this intermediate is added 0.5 parts of dibutyl phosphite. In other examples, a calcium sulfurized phenate (38% diluent oil, 255 total base number) is also present.
PCT publication WO 1987/05927, Oct. 8, 1987, discloses manual transmission fluids comprising, among other components, a selected alkaline earth metal salt. In Example IV, a manual transmission fluid is prepared by combining, with other ingredients, 3.5 parts calcium alkyl benzene sulfonate (overbased) wherein the alkyl contains about 24 carbon atoms on average. In a description of overbased salts, it states that typically, the excess alkaline earth metal will be present over that which is required to neutralize the anion at about 10:1 to 30:1, preferably 11:1 to 18:1 on an equivalent basis.
U.S. Pat. No. 6,617,287, Gahagan, Sep. 9, 2003, discloses manual transmission lubricants with improved synchromesh performance. Problems of wear and too low friction for a manual transmission with sintered metal parts in the synchronizer are said to be solved by using a lubricating oil formulated with a high level of an alkaline earth sulfonate in combination with amine phosphates. Preferred metal salts are magnesium or calcium, more preferably magnesium. The overbased materials generally have a total base number from about 20 to about 700, preferably from about 100 to about 600, and more preferably from about 250 to about 500. In examples, there is employed an overbased magnesium alkylbenzenesulfonate with a TBN of 400 and containing about 32% mineral oil diluent.
U.S. Patent Publication 2008/0119378, Gandon et al., May 22, 2008, discloses functional fluids comprising alkyl toluene sulfonates as friction modifying agents. The fluids may be tractor fluids, transmission fluids, or hydraulic fluids. The alkyl toluene sulfonate salts may be either neutral or overbased salts, and they may be highly overbased to have a TBN of between about 50 to about 400, or about 280 to about 350, or about 320.
European Patent Application EP 0 552 863, Jul. 28, 1993, discloses high-sulfur mineral oil compositions and reducing the copper corrosivity of mineral oils having a high content of sulfur compounds. Example 1 discloses an additive concentrate containing, among other components, 1.33% of an overbased calcium sulfurized phenate, indicted to have a TBN of 254, and 1.33% calcium dinonylnaphthalene sulfonate as a 50% solution in light mineral oil. The lubricating oil compositions can be used in a variety of applications such as automotive crankcase lubricating oils, automatic transmission fluids, gear oils, hydraulic oils, or cutting oils. The preferred application is as power transmission fluids, especially hydraulic oils.
U.S. Pat. No. 4,792,410, Schwind et al., Dec. 20, 1988, discloses a lubricant composition suitable for manual transmission fluids. Example II discloses a manual transmission fluid containing, among other components, 3.0 parts calcium alkyl benzene sulfonate (overbased). Example III includes 3.5 parts calcium sulfur coupled alkyl (C12) phenate overbased to 200 total base number.
PCT publication WO 2000/26328, May 11, 2000, discloses lubricants having overbased metal salts and organic phosphites. The lubricants may be used in manual transmissions. Example 1 discloses a lubricant prepared by blending (with other components) 0.7% of a calcium benzene sulfonate having 53% oil and a total base number of 41.
European Patent Application EP 0 987 311, Mar. 22, 2000, discloses transmission fluid compositions. A composition comprising an oil and (among other components) at least 0.1 percent by weight of an overbased metal salt provides an improved fluid for continuously variable transmissions. It is said that manual transmission fluids (among others) can benefit from incorporation of the components of that invention. Example 5 discloses a mixture of components including 0.3 parts overbased calcium sulfonate, including 0.1 part diluent oil (300 TBN). The suitable overbased materials themselves preferably have a total base number of 50 to 550, more preferably 100 to 450, on an oil free basis.
U.S. Pat. No. 3,652,410, Hollinghurst et al., Mar. 28, 1972, discloses lubricant compositions for a multipurpose lubricating oil that can be used for, among others, transmissions. Examples in Table I contain basic calcium sulfonate total base No. 300.
U.S. Pat. No. 7,238,651, Kocsis et al., Jul. 3, 2007, discloses a process for preparing an overbased detergent and the use of such a detergent in internal combustion engines. An example discloses the preparation of 500 TBN calcium sulfonate. The Total Base Number is described as a measure of the final overbased detergent containing the oil used in processing. Various optional performance additives may also be present.
U.S. Patent Publication 2010-0152080, Tipton et al., Jun. 17, 2010, discloses a lubricant composition exhibiting good dynamic frictional performance. The lubricant composition comprises an oil of lubricating viscosity and an oil-soluble branched-chain hydrocarbyl-substituted arenesulfonic acid salt having at least one hydrocarbyl substituent which is a highly branched group as defined by having a Chi(0)/Shadow XY ratio greater than about 0.180.
U.S. Pat. No. 5,635,459 (Stoffa et al., published 3 Jun. 1997) discloses functional fluid composition having improved gear performance comprises an oil of lubricating viscosity, and added thereto (a) an alkali or alkaline earth metal salt complex in the form of borated and/or non-borated salts; (b) an EP/antiwear agent comprising a mixture of zinc salts of dialkylphosphorodithioic acid and 2-ethylhexanoic acid heated with triphenyl phosphite or an olefin; and (c) a borated epoxide.
U.S Publication 2009/0203564, Seddon et al., Aug. 13, 2009, discloses a process for preparing a neutral or an overbased detergent. In certain embodiments, the detergent may have a TBN ranging from 100 to 1300, or from 250 to 920. The overbased detergent is said to be suitable for any lubricant composition; listed lubricants include transmission fluids and gear oils, among others.
Lubricants are known which provide a desirable friction for interaction with synchronizers. However, it is desirable to have a lubricant that has desirable friction shift characteristics (such as slope and curvature of engagement) compatible with the material of the synchronizer, but also a lubricant which is durable, such that the level of dynamic friction does not degrade but remains at a substantially constant level over a long period of the transmission being in use. The greater the durability of the friction properties of the lubricant, the wear of the synchronizer and therefore the lifespan of the synchronizer itself will be increased, along with optimized shift performance.